Plural demodulation-circuits



H. S. OSBORNE.

PLURAL DEMODULATION C|RCUITS`| APPLicATloN FILED JAN. s. 1920.

1,861,487', Patented Dec. 7, 1920.

Y J 090mm/ tion at a particular station,

HAnoLD s. osia'onNE, or NEW Yoan, N, Y., AssIeNon To AMERICAN rnmn'onn i 'rELEenArncoMrm, A eonPonArIoNioF New Your rLUnAL DMoDuLArIoN-cmcuxrs. r

Application med January e, V1920. serial No. $49,738',

To all'whom ztmay concern.' Be; it known that 1,'HAR0LD S. jOsBoRNE, resldmg at New York, in the county of New York and State of New York, have invented lates tothe provision of a-method of separat-v ing a narrow band of frequencies for recepassuming that a large range of frequencies is in use and that only a small part of this range is to be se- I lected. i

cles said frequencies with a frequency Another feature oi the invention resides in a method of selection which comprises receiving the desired band of frequencies, together with undesired frequencies, beating lower than the desired band, selecting from the resultant frequencies a band corresponding to the desired band lowered in the frequency spectrum and then successively stepping down the frequency of this band in a plurality of steps, to a frequency range sufficiently low for eicient selection ofindividual frequen- A still further feature of the invention residesV in a method of selective receiving, which consists in impressing the desired band of frequencies, together with undesired frequencies, upon a circuit tuned to a frequency which is approximately a mean of the limiting frequencies of the desired band, beating the received frequencies with a lof callv supplied frequency as close as possible to the desired band. but suicientlv remote therefrom so that of the frequencies lying in a band corresponding to the desired band at a lower position in the frequency spectrum. those frequencies which resulted from the reaction of undesired frequencies with the locallv supplied frequency will be of very small amplitude as compared with those frequencies resulting from the reaction of the frequencies in the desired received band with said locally supplied frequency.

Other features of the method involved in this invention will be flear from the following concrete statement of the method. Let it be assumed that at a given station it is desired to select all frequencies lying between If the selection were to be made by the ordinary methods of discrimination now practiced in the radio wrt .this would involve excluding such frequencies as 599,500 and 610,500 cycles, which 'would be practically Patentedqljem '7,

600,000 `and 610,000 cyclesfand to exclude all frequencies. lying outside of that range.`

impossible. It is therefore proposed .to impress the vvarious received frequencies upon a circuit tuned sharply toabout 605,000 cycles, which, it will benoted, is practically the mean ofthe limiting'v frequencies of the desired band. Since the desired -band is drelatively narrow as compared -with the range of frequencies. extending from zero up t'o thefd'esired frequency, this step would g1ve 'practically uniform reception for the frequencies `between 600,000 and 610,000 cycles anddecreasing reception for other frequencies. Such a circuit might, for example, give only ten per cent. reception of current 0f 550,000 cycles. 1

The next step of the method involves beating lthe various frequencies with a locally supplied frequency for the purpose of 'step-l ping down the frequency of the desired band. The locally supplied frequency should be chosen as close-as possible to the desired b'and and should be sufficiently below said band, so that frequenciesresulting from the reaction of the local frequency with the undesiried frequencies' will,I if they -fall within the limits of the band resulting this would reduce the desired 'l and 60,000 cycles4 would also be'produced by the reaction of the locally supplied 550,000 cycle currents with received currents in the range between 500,000 and. 490,000 cycles, since the last mentioned band of frequencies is quite distant from the frequency to which the first circuit is tuned, the .resultant frequen' ies between 50,000 and 60,000 cycles will be of very small amplitude as compared with frequencies Within the same range resulting frcmthe stepping down of the desired band of frequencies.

` output circuit of the demodulator D1. This i After stepping' down the. desired band of frequencles and filtering inthe manner just described, the resultant band `may be again stepped down b beatlng with locally supplied currents o a lower frequency which should be chosen with regard to the same considerations as stated in connection with the first step of lowering frequency. If it be assumedv for purposes of illustration, that' the second ocally supplied frequenc be 40,000 cycles, its reactance Wlth the se ected band would reducethe frequencies of said band to the range between 10,000 and 20,000 cycles. This range would then again be passed through a band filter.

The process may be contmued Ias many times as may be necessary to pick out the high frequencies desired. In the 4case supposed, probably 'a third ste ping down of the frequenc would be su cient. For 1nstance, if t e band between 10,000 and 20,000 cycles is beaten with a locally supplied lfrequency of 10,000 cycles, the. currents will then lie in the frequency range from zero to 10,000 cycles and interfermg currents would be eliminated.

One form of ap aratus for carl' lng out the method may Ee understood rom the following description when read in connection with thel accompanying drawing, the figure of .which illustrates apparatusl of a radio receiving system.

Referring to the figure, RA designates .a receiving antenna of ordinary construction, which is coupled through a transformez" 10 with a tuned circuit 11. Where, for instance, the desired band of frequencies lies between 600,000 and 610,000 cycles, the antenna and the circuit 11 may both be jtuned lator 1 of a well-known type, is ar nged with its input circuit connected to the l uned circuit 11 and a local beating frequencymay be impressed upon said in ut circuit by means of a connection 12 leading to a geilerator Gr1 which supplies a frequency of 550,000 cycles, of this type, as is well known, produces in its output circuit frequencies corresponding to the sums and differences of the frequencies applied to its input circuit, consequently a frequency band between 50,000 cycles and 60,000 cycles will appear in its output circuit, corresponding to the reaction of the locally supplied frequency of 550,000 cycles vwith the desired received frequency band ranging from 600,000 to 610,000 cycles.

A band filter F1 is connected with the to 605 000 cycles. A vacuum tube dnodufilter may be of the type' disclosed in the U. S. patents to George A. Campbell, Nos. 1,227,113 and 1,227,114, The filter should be designed in accordance with the principles of Said Campbell patents, so as to freely-transmit frequenfor instance.' A demodulator issued May 22, 1917.V

' which 1s substantially a frequencies of the desired band, beating the cies lying between 50,000 and 60,000 cycles,

while su ressin fr uenpies l in without these linillts. Tlgis fillter'may iibvgiously be replaced b ordina tuned circuits.

A secon demodu ator D similar in type to the demodulator D11, has its input circuit associated with thefilter F1. Low beatingI4 oscillations may be supplied over a circuit between'10,000 c cles an 20,000 cycles, vsai band corresponding to the band passed by the filter F1 stepped down to a lower position in the frequency spectrum. A filter F2,

in general siml ar to the filter F1, but havin a free transmission range between 10,000 anc 20,000 cycles, is associated with the output circuit of the demodulator D2 for selectlng this band of frequencies. A third demodulator D, has its input circuit associated with the filter F2 and is supplied over a circuit 14 with local oscillations rom a generator Ga. The frequency of these oscillations may be, for instance, 10,000 cycles. The action of this demodulator will step the band passed by the filter F2 down to a range from zero to 10,000 cycles in the frequency spectrum. A filter F, of the Cam bell type may be provided for selecting t is band to the exclusion of the `other a band lying be-l individual frequencies or groups of frequencies may be selected from this band byv tuned circuitssuch as 16, 17 and 18 and may be impressed upon the circuits of detectors such as D4, D5 and-D, of any well known c aracter. These detectors function to detec the selected frequencies so that the may actu te the receiving devices such as 1st R and e of any well known t e.

It will be understood that the fre uencies hereinbefore described vare merely ilustrative and may be varied inpractice as conditions may require, l

lIt will also be understood that the details of the method herein set forth ma be varied and that the general principles herein disclosed may be embodied in many other or ganizations widely different from those illustrated, without departin the invention as define claims.

What is claimed is:

in the following 1. The method of radio signalin which from the spirit of cies, upon al circuit tuned to a frequency mean of -the limiting received frequencies with a locally supplied Aconsists in stepping received radio frequency which is as close as possible to the desired band, but sufficiently remote there- ,from, so that of the frequencies in the repared with that of the other frequencies in the band. which are-theresult of the reaction of the locally supplied frequency with the desired received band of frequencies.

2. The method of radio signaling which consists in stepping received radio frequencies, including a desired band of frequencies and undesired frequencies, to a lower level in the frequencyv spectrum, selecting from the lowered range vof frequencies the desired band, then successively stepping down the selected band to a low position in the frcquency spectrum by a plurality of steps.

3. The method of radio signalin which frequencies, including a desired band of frequencies and undesired frequencies to a lower level in the frequency spectrum, selecting from the lowered range of frequencies the desired band, then successively stepping down the selected band to a low position in the frequency spectrum by a plurality of steps, and selecting into different channels desired frcquencies from the band thus stepped down.

4. The method of radio signaling which consists in receiving a desired band of radio frequencies together with undesired frequencies, beating the received frequencies with a frequency below the desired band, selecting from theI resultant frequencies a band corresponding to the desired band lowered in the frequency spectrum, successively beating the selected band with a plurality of still -lower frequencies and finally selecting the desired band in its resultant low position m the frequency spectrum.

In testimony whereof, I have signed my name to this specification this 3rd day of January 1920.

HAROLD S. OSBORNE. 

